The present invention relates to a traction vehicle for ground movement of an aircraft, having at least one nose wheel, which traction vehicle comprises
a wheel-mounted chassis and
an engagement and hoisting device that can be raised and lowered relative to the chassis and is of a type that is brought into freely carrying engagement with the nose wheel and which comprises
a stand, being substantially U-shaped with its opening turned towards the aircraft,
journalling members, flexibly connecting the stand to the chassis,
actuators, arranged between the stand and the chassis to raise and lower the engagement and hoisting device relative to the chassis, and
a nose-wheel holder, having
an inner space that can be opened in the direction of the nose wheel for receiving the same,
carrying members for carrying the nose wheel in said space, and
forward and rear wheel supports for holding the nose wheel in the longitudinal direction of the traction vehicle.
The invention also relates to such an engagement and hoisting device.
Once the maximum steering angle of an aircraft has been attained, whilst moving the aircraft on the ground with the aid of a traction vehicle coupled to the nose wheel of the aircraft, when the direction of travel of the traction vehicle is changed, torque is transferred to the nose-wheel stand via the nose wheels and its upwardly-directed steering or rotary axle. This torque must not exceed prescribed values laid down by the various aircraft manufacturers in question. In the following, this maximum permitted torque is referred to as the maximum torque or maximum value.
A traction vehicle in accordance with the preamble to claim 1 is known through SE-500 744. The engagement and hoisting device supported by the chassis of the traction vehicle is arranged to be brought into a starting position close to, but not touching, the nose wheels of the aircraft, both in front of and behind the contact point between the nose wheels and the ground, when the traction vehicle is moved relative to the nose wheels, and to be raised from said starting position in order, when in free surface contact with the nose-wheel tread on both sides of said contact point with the ground, to be brought into releasable engagement with the nose wheels so that the same are lifted from the ground when the engagement and hoisting device is raised. The engagement and hoisting device forms a rigid connection between the nose wheels and the chassis. Thus, to enable a change of angle between the traction vehicle and the aircraft, the steering hydraulics of the aircraft must be disconnected and the rotary movement of the nose wheels limited by mechanical terminal stops on the aircraft. At these terminal stops, the aircraft has attained its maximum steering angle and torque will be transmitted to the nose-wheel unit, via the rotary axle of the nose wheels, wherein, as mentioned above, the torque value must not exceed a maximum value determined by the manufacturers of the aircraft. Exceeding the maximum torque without forewarning presents a very great risk of the nose-wheel unit being damaged. SE-501 788 describes a device for measuring and indicating the steering angle of the aircraft relative to the traction vehicle in order, thereby, to prevent the nose-wheel stand being subjected to the harmful maximum torque. However, such a device has the disadvantage that, for instance, a sensor wire must be connected to the aircraft. As designs differ from one aircraft to another, it can be difficult to provide equipment to suit all the types of aircraft a traction vehicle must be able to handle.
In another type of traction vehicle, the same is connected to the aircraft with the aid of a traction rod, where torque is limited with the aid of a breakpin in the traction rod or in the fastening of the traction beam to the nose-wheel stand. A disadvantage with this system is that no forewarning is provided before the pre-set torque is exceeded so that the traction vehicle must be substituted or the traction rod replaced. In addition, there is a risk of the nose-wheel stand being damaged because the traction rod is released from the aircraft in some cases.
U.S. Pat. No. 4,576,245 describes a tractor for towing a helicopter or medium-sized aircraft. The tractor has an engagement and hoisting device that can be raised and lowered and consists of a wheel-borne chassis, formed by two beams and a platform mounted thereon, and also a support plate, pivotably journalled on the platform by means of a thrust bearing and intended to support the nose wheel. The support plate has an upright with a hydraulic cylinder, the piston rod of which is provided with a yoke with screws for securing the piston rod to the nose wheel. The helicopter is drawn towards the tractor with the aid of the hydraulic cylinder so that the nose wheel rolls onto the lowered platform to be received on the support plate and retained thereon with the aid of the hydraulic cylinder. Thereafter, the chassis is raised to its towing position. WO 98/25822 describes a tractor for towing an aircraft. The tractor has a platform for carrying the nose wheel. The aircraft is moved forwards towards the platform, whereupon the nose wheel is moved onto the platform with the aid of a ramp. The platform can be provided with a rotary plate on which the nose wheel rests. However, the WO specification does not show any device for retaining the nose wheel on the rotary plate and platform. The platform is arranged such that it can perform a swinging or pendulum movement relative to the chassis in the longitudinal direction of the tractor from a resting position. When the aircraft is moved on the ground, the deviation of the swinging or pendulum movement from the resting position is a measure of the load on the nose wheel in the horizontal and vertical direction. By measuring the swinging or pendulum movement with a linear-movement or angle transducer, the load can be kept within prescribed values by limiting the acceleration or retardation of the tractor when too great a deviation from the resting position is measured. The known traction vehicles in accordance with U.S. Pat. No. 4,576,245 and the WO specification 98/25822 are of a type completely different from the one to which the invention refers. Unlike the traction vehicle in accordance with the invention, they cannot be used for aircraft of varying sizes and they are not intended to be docked to the aircraft. They lack, and cannot be provided with, an engagement and hoisting device that can be raised and lowered relative to a chassis and has a U-shaped stand to enable said docking to a stationary aircraft and provide freely supporting engagement with the nose wheel with the aid of a special nose-wheel holder, the engagement and hoisting device being raised to lift the nose wheel from the ground.
The object of the present invention is to provide a traction vehicle with an improved engagement and hoisting device that enables security demands from aviation authorities or operative or functional demands from users to be met so that an improved control of and security during the ground movement of the aircraft is obtained, as compared with known traction vehicles.
The traction vehicle, as well as the engagement and hoisting device, is characterised in
that the nose-wheel holder and the stand are shaped as two separate units and comprise co-operating journalling members, arranged in a circular arc and defining a vertical axis of rotation for said units and
that the nose-wheel holder is substantially U-shaped with its opening turned towards the aircraft as viewed in a starting position, when the nose-wheel holder is situated to be moved into a position to receive the nose wheel.